1. Field of the Invention
The present invention generally relates to an alternating current or AC generator destined for use in an automobile or motor vehicle (hereinafter, this type generator will also be referred to as the vehicle-onboard AC generator). More particularly, the present invention is concerned with an improvement concerning an arrangement for interconnection of stator windings of the vehicle-onboard AC generator.
2. Description of Related Art
Before entering into description of the vehicle-onboard AC generator according to the present invention, technical background thereof will be reviewed in some detail for having better understanding of the concept underlying the invention. FIG. 15 is a sectional view showing a conventional AC generator which has heretofore been known. Referring to the figure, the illustrated AC generator is comprised of a housing or case 3 made of aluminum, which case includes a front bracket 1 and a rear bracket 2. A shaft 6 is rotatably mounted on the brackets 1 and 2 by means of roll bearings within the case 3, and a pulley 4 is mounted at one end thereof. A landaulet type rotor 7 is fixedly mounted on the shaft 6 for corotation therewith. A pair of fans 5 are fixedly secured to both surfaces, respectively, of the rotor 7 for the purpose of cooling. A stator 8 is stationarily mounted on an inner wall of the case 3. A slip ring 9 is fixedly mounted on the shaft 6 at the other end portion thereof for supplying an electric current to the rotor 7. A pair of brushes 10 are disposed in slidable contact with the slip ring 9. A brush holder 11 is so disposed as to accommodate therein and support the brushes 10. A rectifier device 12 is electrically connected to the windings of the stator 8 for rectifying an alternating current induced in the stator windings into a direct current. A heat sink 17 is physically coupled to the brush holder 11. Further, a regulator 18 is fixedly secured onto the heat sink 17 for adjusting or regulating the magnitude of an AC voltage induced in the stator winding assembly.
The armature rotor 7 is composed of a rotor coil 13 through which a direct current supplied from a battery (not shown) is caused to flow for generating magnetic fluxes. A pole core is so disposed as to encase therein the rotor coil 13 and has magnetic poles formed by the magnetic fluxes. More specifically, the pole core is constituted by a first pole core member 20 and a second pole core member 21 which are complementarily meshed together for thereby constituting the pole core.
On the other hand, the stator 8 is constituted by a stator core 15 and stator windings (also referred to generically as the stator winding assembly) 16 each of which is formed by winding an electric conductor on the stator core 15 and in which an alternating current is induced under the effect of changing of the magnetic fluxes emanated from the rotor coil 13. Incidentally, arrows shown in FIG. 15 represent flows of cooling air generated by the fans 5.
In the vehicle-onboard AC generator implemented in the structure described above, a DC current is supplied to the rotor coil 13 from a battery (not shown) by way of the brushes 10 and the slip ring 9, whereby magnetic fluxes are generated by the rotor coil 13. As a result of this, the first pole core member 20 is magnetized in N-polarity while the second pole core member 21 is magnetized in S-polarity. On the other hand, the pulley 4 of the AC generator is driven by an engine such as an internal combustion engine of the motor vehicle on which the AC generator is installed, whereby the shaft 6 and hence the rotor 7 are caused to rotate in unison. Consequently, the stator windings are exposed to the rotating magnetic fields, which results in generation of an alternating current in the stator winding assembly 16 under the effect of electromagnetic induction. The alternating current as generated is supplied to the rectifier device 12 to be thereby rectified into a direct current, the magnitude of which can be adjusted by the regulator 18. The direct current outputted from the rectifier device 12 is ultimately charged in the battery.
FIG. 16 is a perspective view showing a structure of the stator of the conventional AC generator, and FIG. 17 is an equivalent circuit diagram thereof. Referring to FIG. 16, the stator windings 16 are each formed by winding a round wire conductor and accommodated or housed stationarily within slots formed in the stator core 15. As can be seen in FIG. 16, the stator winding assembly 16 is comprised of lodged portions 161 housed within the slots and coil end portions 162 projecting, respectively, beyond both ends of the stator core 15.
Referring to FIG. 17, the stator windings 16 are interconnected in a star connection in order to realize a three-phase AC generator circuit. End portions of the three conductors led out from the individual windings of the stator winding assembly are connected together to form a neutral point in the form of a neutral point junction 22. Further, interconnecting portions 23 are provided for interconnecting the conductors brought out from the stator windings and terminals of the three-phase rectifier device 12. Further, for the purpose of taking out the output power from the neutral point junction 22, an output power conductor 24 is electrically connected to the neutral point junction 22, although it depends on the design conditions. In that case, the neutral point junction 22 is realized by connecting together the end portions of four electric conductors in total.
In this conjunction, it is further noted that in recent years, there is a tendency that a thick conductor of a large diameter is employed for forming the stator winding assembly in an attempt for implementing the three-phase AC generator having a high output capacity. To this end, a so-called bifilar-winding or W-winding in which a single winding conductor is divided into two coextensive conductors is increasingly adopted. In the case of the stator composed of the bifilar type windings, one neutral point junction 22 is provided at one location on one side, while in the case of the W-winding type, two neutral point junctions 22 have to be provided at two locations on both sides, respectively, as can be seen in FIG. 17. In any case, the output power conductors 24 have to be brought out from the neutral point junction(s) 22.
The output power conductor 24 mentioned above is made of tough pitch copper, and each joint forming the interconnecting portion is realized by soldering. After the soldering, the conductor portions forming the neutral point junction 22 are encased within an insulation tube 25. In succession, the encased conductor portion is laid or bent along the coil end portion to be subsequently fixed by applying a varnish or the like with a view to ensuring a vibration withstanding capability. Of course, the joint described above may be realized by using heterogeneous metal, as disclosed in Japanese Patent Application Laid-Open Publication No. 115743/1995 (JP-A-7-115743).
In the conventional vehicle-onboard AC generator of the structure described above, when interconnection of the conductors brought out from the individual windings has to be made internally of the stator 8, the output power conductor 24 extending from the round wire conductors have to be wired along the circumference defined by the coil end portions 162, involving difficulty in automatization of the wiring by machine.
Further, since the conductor portions forming the neutral point junction 22 are encased within the insulation tube 25 and laid on and along the coil end portions 162 to be subsequently fixed by a varnish, a heat radiation property of these conductor portions is poor when compared with the conductors of other winding portions, incurring high temperature rise. Consequently, thermal deterioration of these conductor portions as well as the adjacent conductor portions is promoted, providing a major factor for degradation of the durability of the stator as a whole.
Besides, the process for securing the connected and tube-inserted conductors onto the coil end portion 162 is difficult to automative, providing a problem in reduction of the cost of processing or treatment.
In the case of the AC generator disclosed in Japanese Patent Application Laid-Open Publication No. 19119/1997 (JP-A-9-19119) a single circuit board is employed for connections/interconnections of all the conductors. In that case, the rigidness of the stator as a whole is increased remarkably, which however means that difficulty will be encountered in correcting positional misalignment between the stator and the rectifier device upon assembling the stator onto the main body of the AC generator. In many cases, the circuit board is forcibly distorted, providing a cause for degradation of the durability. Besides, the work for assembling the AC generator becomes very troublesome. In some case, the circuit board is cracked, to a great disadvantage.
Furthermore, the circuit board disclosed in Japanese Patent Application Laid-Open Publication No. 19119/1997 is equipped integrally with an intermediate connecting member and an output terminal member and thus poor in respect to the cooling performance, exerting adverse influence to the temperature characteristics or behavior of the rectifier device. Besides, upon occurrence of a short-circuit fault, the connecting terminal member implemented in a large length and thus exhibiting high electrical resistance gives rise to another problem that relevant molded portions are burnt under the heat generated due to a large short-circuit current. For these reasons and because of spatial restriction imposed on the circuit board, realization of the vehicle-onboard AC generator with high output capacity encounters unavoidably a limitation.
In the light of the state of the art described above, it is an object of the present invention to provide a vehicle-onboard AC generator of an improved structure which allows the process for assembling the stator of the AC generator to be easily automatized for rationalization of the AC generator manufacturing process while ensuring positive suppression of heat generation as well as enhanced cooling performance in operation of the AC generator.
In view of the above and other objects which will become apparent as the description proceeds, there is provided according to an aspect of the present invention a vehicle-onboard AC generator which includes a stator comprised of a stator core and a stator winding assembly including a plurality of stator windings, a rotor disposed in a state enclosed by the stator core, and a rectifier device for rectifying an AC power taken out from the stator winding assembly, wherein in the stator, a plurality of outgoing conductors forming output conductor end portions and connecting conductor end portions, respectively, are brought out substantially in parallel with a center axis of the stator core. The connecting conductor end portions are connected to an intermediate connecting member provided independently from the rectifier device and disposed on the stator at a position offset laterally from the center axis thereof. The stator windings are interconnected in a predetermined connection pattern through the medium of the intermediate connecting member. The output conductor end portions through which the AC power is taken out are connected to corresponding terminals of the rectifier device.
By virtue of the stator structure in which the intermediate connecting member is employed for interconnecting the stator windings in a predetermined connection pattern such as the star connection, as described above, the wiring process to be performed internally of the stator which will otherwise be required can be spared, to an advantage. More specifically, the processes for interconnection of the winding end conductors, insertion of the conductors in the insulation tubes, securing of the tube-encased conductor portions to the stator coil end portion and others which are difficult to automatize can be spared. This feature in turn contributes to rationalization of the manufacture of the vehicle-onboard AC generator, to a further advantage. To say in another way, since the wiring process which has heretofore been required can be spared owing to provision of the intermediate connecting member (or wiring terminal member) as the terminals dedicated to the wiring for interconnection of the stator winding end conductors in the circuit board of the rectifier device, the manufacturing cost on the whole can be reduced remarkably because of rationalization of the manufacturing process although the material cost increases to some extent due to increase of the number of parts.
Additionally, because heat generation in the coil end portions of the stator winding assembly can be suppressed with the cooling susceptibility of the AC generator being thereby enhanced, high reliability can be ensured for the operation of the vehicle-onboard AC generator.
Besides, because the intermediate connecting member is neither physically connected to the stator nor implemented integrally with the stator and because the intermediate connecting member is provided independently or separately from the rectifier device, a distortion force which would be applied to the rectifier device upon assembling of the stator in the main body of the AC generator can be mitigated, whereby assembling efficiency can be enhanced while the possibility of the circuit board being unwantedly cracked can positively be excluded.
Furthermore, since the intermediate connecting member is provided independently or separately from the rectifier device, the intermediate connecting member can be so disposed that the metal portion thereof is exposed exteriorly, which contributes to enhancing the cooling susceptibility of the stator and hence that of the AC generator.
In a mode for carrying out the present invention, a neutral point output conductor which is connected to the rectifier device should preferably be formed by the connecting conductor end portions as well.
Owing to the arrangement mentioned above, the structure for taking out the AC output power from the neutral point can easily be implemented, which also contributes to increasing the efficiency of generator manufacturing process.
In another mode for carrying out the present invention, the intermediate connecting member should preferably be implemented as a wiring terminal member which is formed of a same copper series metal as a wiring conductor.
By forming the intermediate connecting member of a same copper series metal as the winding conductor which exhibits a high electric conductivity, heat generation brought about upon rectification can be suppressed, whereby the temperature is prevented from rising excessively.
In yet another preferred mode for carrying out the present invention, the wiring terminal member may be molded.
By covering or coating the wiring terminal member with a resin or the like material, the surface of the wiring terminal member which faces oppositely to the cooling fan can be made smooth, whereby generation of disturbing noise can be suppressed significantly. Besides, corrosion resistance of the wiring terminal member can be increased.
In still another mode for carrying out the present invention, the wiring terminal member should preferably be secured fittingly in a circuit board on which at least said rectifier device is implemented.
Owing to the arrangement described above, possibility of the wiring terminal member being inadvertently removed in the course of assembling the AC generator can positively be excluded. Thus, the manufacturing efficiency can be enhanced. Further, the existing manufacturing equipment can be used without modification. Besides, since the wiring terminal member is secured fittingly as described above, it is possible to suppress generation of noise due to resonance which may take place between the circuit board and the wiring terminal member during operation of the AC generator. Thus, an enhanced vibration withstanding capability can be ensured for the AC generator.
In a further preferred mode for carrying out the present invention, the wiring terminal member should be welded to an insert terminal member in advance to be subsequently molded.
The structure mentioned above can profitably be applied to the AC generator of a relatively low capacity. Since the wiring terminal member is made integrally with the insert terminal member in advance by resistance welding or fusion welding, the process or step for mounting or inserting the wiring terminal member formed as a discrete member can be spared, whereby the generator assembling efficiency can be enhanced significantly.
In a yet further preferred mode for carrying out the present invention, the wiring terminal member may be made of a metal plate undergone a surface treatment.
Owing to the feature mentioned above, the wiring terminal member is imparted with a high corrosion withstanding capability. Thus, high reliability of operation can be ensured for the AC generator over an extended use life thereof.
In a still further preferred mode for carrying out the present invention, the wiring terminal member may be made of a bare copper wire.
By employing the wiring terminal member constituted by the bare copper wire, the wiring or interconnecting structure can be realized inexpensively with the yield of manufacture being increased.
In another preferred mode for carrying out the present invention, the wiring terminal member may be implemented in a structure having an L-shaped cross-section.
By forming the wiring terminal member in the L-like shape in cross-section, the mechanical strength thereof is increased, whereby the reliability of the AC generator can be enhanced correspondingly.
In yet another preferred mode for carrying out the present invention, the connecting conductor end portions may be provided with round terminals, respectively, wherein connection of the connecting conductor end portions with the intermediate connecting member is realized by means of screws.
With the arrangement described above, works involved in the connection are simplified and facilitated, which can enhance the efficiency of assembling the AC generator. Besides, the electrical and mechanical connection of high reliability can be realized.
In still another preferred mode for carrying out the present invention, the output conductor end portions may also be provided with round terminals, respectively, wherein connection of the output conductor end portions to the rectifier device is realized by means of screws.
With the arrangement described above, works involved in the connection are simplified and facilitated, which can enhance the efficiency of assembling the AC generator. Besides, the electrical and mechanical connections of high reliability can be realized.
In a further mode for carrying out the present invention, each connecting portion of the intermediate connecting member for connection with the connecting conductor end portions should preferably be implemented in the form of a U-like segment, and the connecting conductor end portion may be fixedly secured to the U-like segment through press fitting.
With the arrangement described above, work for connecting the connecting conductor end portions to the intermediate connecting member is facilitated, whereby efficiency of assembling the generator is enhanced while ensuring high reliability for the connection.
The above and other objects, features and attendant advantages of the present invention will more easily be understood by reading the following description of the preferred embodiments thereof taken, only by way of example, in conjunction with the accompanying drawings.